At 02:04 PM 1/18/01 -0800, [EMAIL PROTECTED] wrote:

>the rotation stations could
>somehow count or limit the number of photons going through so that they
>would know when there were extra.  I think this is possible in theory;

Right, it is.  Here's a Gedankenexperiment:  temporarily trap the signal in 
a cylindrical waveguide resonator (organ pipe).  The pressure on the 
end-caps is proportional to photon number and independent of polarization 
angle.  From this we conclude we can measure number in a way that commutes 
with polarization.

I went overboard when previously I said "any" attempt at integrity-checking 
would mess up the signal.  Still, integrity-checking of a single photon 
would be hard.

>  I don't think she could learn much with a single photon,

I'm not so sure about that.  Remember, photon counters (which measure 
A_dagger A) are not the only measuring devices in the world.  There are 
also voltmeters (which measure A_dagger plus A).  For low-amplitude analog 
signals, the voltmeter is vastly more informative.  I have not yet cobbled 
up a believable apparatus for measuring the polarization angle of a single 
photon, but I don't think it would be terribly hard to do so.

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